Statistical analysis and normality of selected hematologic and clinical chemistry measurements used in toxicologic...

The statistical comparison of hematological and clinical chemistry measurements of treated and control groups in toxicological studies has frequently, in the past, been done by methods that assumed, in the population of such values, normality of the data. This assumption was tested on pairs of concurrent control groups of rats from three long-term toxicological studies; two feeding and one inhalation routes of exposure were used. The normality of the data from three treated groups in one of these studies was also tested. The measurements examined were erythrocyte count, hemoglobin, white blood cell count, neutrophils, monocytes, urea nitrogen, and creatinine. In many cases significant skewness, kurtosis and deviation from normality as measured by the Kolmogorov-Smirnov test were present. The lack of consistency of normality versus nonnormality or, in some cases, direction of skewness, suggests that nonparametric statistical procedures be considered for use in the future for comparison of these types of data. Furthermore, the agreement of the data of the concurrent control groups as compared to the divergence of the values among the three studies affirms the importance of concurrent, in preference to historical, control data.